Detection of chemical compounds can be performed by ionizing substances in air at ambient pressure and characterizing ions contained in the substances. Performing this characterization in air at ambient pressure allows for use of inexpensive and robust analyzers. Such detection methods are used today in, for instance, ion mobility spectrometry (IMS) and differential mobility spectrometry (DMS).
In the traditional method of drift-time IMS, commonly referred to as just IMS, ions obtained from a substance travel through a drift chamber, which has an applied electric field that affects ion trajectory and a carrier buffer gas that opposes ion motion. At the end of the drift chamber is a detector. An ion's mobility is a function of its mass, charge, size, and shape. As a result of different ion mobility of different ions, migration time through the drift chamber of each type of ion is different, leading to the ability to distinguish different ion species.